In recent years, with the progress of miniaturization of a very large scale integration (VLSI) process, technologies related to miniaturizing semiconductor devices and constructing the devices three-dimensionally have been developed. This increases the number of thin films that can be stacked. For example, a flash memory using a 3D NAND requires a process of dry-etching a thick laminated film having a thickness of 1 μm or more, including a silicon oxide (SiO2) film. During the dry etching, conventionally, amorphous silicon or amorphous carbon is used as a hard mask. However, the amorphous silicon or the amorphous carbon has insufficient etching selectivity with respect to an SiN/SiO composite film constituting a target etching layer, leading to insufficient dry etching resistance.
As such, the development of a new hard mask material having high dry etching resistance and high etching selectivity is required. A boron-based film has various excellent properties such as high dry etching resistance and low dielectric constant as an insulating film material, and thus, the application of the boron-based film to various applications (uses) has been reviewed. For example, the application of a boron nitride film as a boron-based film to a hard mask during etching is known. However, among boron-based films, a boron film has diverse possibilities but has rarely been applied to semiconductor devices.
In addition, in order to form a vibrator for an electroacoustic transducer with boron, a technique of forming a boron layer on a sprayed coating of boron or a boron compound at a temperature of 900 to 1,200 degrees C. using a mixture gas of boron trichloride and hydrogen as a raw material gas by a chemical vapor deposition (CVD) method is known. In addition, a technique of heating a gas mixture obtained by blowing an inert gas in a mixture of a borane complex and an inert organic medium and thermally decomposing the borane complex at a temperature of 200 to 600 degrees C. to deposit boron on a substrate is known. These techniques, however, do not relate to a semiconductor device.
Moreover, a basic research related to the formation of a boron film on a silicon substrate using a plasma CVD has been conducted but conditions for forming a boron film suitable for a hard mask have not been disclosed.
In addition, there is a technique for forming a film called “boron-rich film” used as a hard mask or the like. In this technique, it has been found that, in the boron-rich film, the content of boron is greater than 60% and the content of other components such as hydrogen, oxygen, carbon, nitrogen and the like is within a range of 1 to 40%. Further, it is has been found that the content of the other components can be less than 5% when the boron-rich film is used as a hard mask.
This technique, however, merely shows the formation of a boron-rich film containing boron within a concentration range of 54 to 66% and results obtained by evaluating its characteristics, without presenting an example. Thus, it is not clear whether it is actually possible to form a boron-rich film containing boron of a higher concentration based on such a technique.
Furthermore, according to the results obtained by performing a Fourier transform infrared spectroscopy (FTIR) analysis on a boron-rich film having a boron concentration of 54%, peaks corresponding to plural kinds of bonds such as B—OH (boron-hydroxy group bond), B—H (boron-hydrogen bond), and B—N (boron-nitrogen bond) were recognized, and among them, a maximum peak corresponded to B—N. This means that the boron-rich film actually formed based on the related art is merely a boron nitride film used as the conventional hard mask.